This invention concerns a vane-surrounding member of an airmotor. More specifically, it relates to a rotor, a cylinder, a front cylinder cover, a rear cylinder cover or the like in contact with a vane type air motor, applied with a surface treatment by using a bright nitrogen diffusion method.
Vane type air motors are simple and convenient to handle with and have been generally used for such application uses as small-sized clamping apparatus. Particularly, since they have an advantage of being usable conveniently in a working circumstance which may cause danger upon occurrence of electric sparks so long as a high-pressure air source is available, without using an explosion proof motor.
Vanes made of die steels or high speed steels have been used so far for the vanes of the air motors but, since motor vane rotate at a high speed, the surface of vane-surrounding members undergo repetitive contact with the vanes and, as a result, tends to cause defects such as abrasion, injury or scorching. Accordingly, in the existent vane-surrounding members for the air motors, quenching/tempering, nitridation and soft nitridation for surrounding members have been applied and, further, oil-feeding operation such as of turbine oils has been indispensable for preventing occurrence of such defects.
However, since the hardness on the surface of the vane-surrounding members is insufficient or nitrogen compounds constituting the nitridation layer tend to be defoliated in the treatment, the working life of the vane-surrounding members is extremely short and the productivity is poor since the conditions for manufacturing the nitridation layer are difficult. Further, while surrounding members comprising super hard alloys may also be used in addition to the die steels or high speed steels described above, they are expensive as the material for the members and, in addition, involve a problem that they are more fragile compared with the die steels or high speed steels, so that they involve inconvenience that they can not be applied to products having thin or complicated shapes, for which improvement has been demanded. Further, as industrial situations, manual oil feeding operation has been disliked and oilless motors not requiring oil feeding operation has been demanded in recent years in view of circumstantial sanitation.
In view of the foregoing situations, this invention has a subject of providing a long life vane-surrounding member for air motors excellent in abrasion resistance, impact resistance and thermal shock resistance having higher hardness for the surface of the vane-surrounding member than usual.
A member for air motors defined in claim 1 has a feature in which a surface is heated to 450 to 580xc2x0 C. in a mixed gas atmosphere comprising 50 to 95% of hydrogen, and 5 to 50% of nitrogen and hydrogen sulfide, a DC voltage at 300 to 500 V is applied relative to an anode disposed in a vacuum chamber, and a nitrosulphurization layer is formed on the surface by using a bright nitrogen diffusion method.
A member for air motors defined in claim 2 has a feature in which the nitrosulphurization layer has a hardness of 800 to 1200 Vickers hardness (load: 100 gf).
A member for air motors defined in claim 3 has a feature in which the ratio of nitrogen and hydrogen sulfide in the gas mixture is from 0.01 to 99 parts by volume of hydrogen sulfide based on 100 parts by volume of the nitrogen content.
A member for air motors defined in claim 4 in which the member is one or more of rotors, cylinders, a front cylinder covers or rear cylinder covers.